The  CAP800-70  Amplifier
New Repeater Build


This is the NEW final amplifier that is going to be installed in the 442.650 repeater to replace the final tube amplifier.  The CAP800-70cm amplifier is capable of 800 Watt output, 100% duty cycle, and all mode operation for UHF (420-450Mhz) which we will run at around 300 watts.  This pallet is built on a copper heat spreader with a gold plated printed circuit board, utilizing the latest 50V LD-MOSFET technology.  Like the amplifiers used in the Broadcast industry this pallet is for continuous 100% duty cycle.

We are using a HP model ESP-120 power supply to run the amplifier which is capable of 51Volts at 57Amps with a 220VAC input.

We are building it in a stripped TE System rack-mount amplifier deck.


The reason for this build is the cost of the final tube used in the repeater (3CX400A7) has now starting to push $800.00 for a new one and harder to find.  Since we only seem to get 1 to 1 1/2 years usage out of a new one we need to find an alterative.  We have also purchased pulls in the past, but of course don't get as long of a usage time out of them which is expected.  We just purchased a pull two months ago and have no more back-ups for replacement if the current tube starts to go bad.  With the cost of tubes and a costly tower work we have done the last year we don't have the money to purchase a back-up at this time.  So rather then putting more money (we don't have) into purchasing tubes ... it makes sense to change things out to something different that should stop the bleeding of cash for tubes !!  This project will cost about $1000.00 total when completed and a extensive modification of the Motorola repeater removing the high-voltage power supply, the final high-power tube final assembly, and rewiring.



Below are a few pictures of the construction of this pallet amp.
(click on small pictures to enlarge)



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We have had a change of plans and have now decided to build a completely NEW 442.65 Repeater !  We will discontinue the operation of the Motorola repeater package which is over 35 year old technology that we have had in service for around 15 years now. We are going to build a totally NEW Kenwood based repeater package.

So stay tuned and come back here for more information & pictures as we start construction, which should be very soon !!





Here is most of the equipment and cabinet for the new build ready to start construction. 


Here  We  Go !!


Changed a few thing around to there final locations and started some wiring !
(Power supply is mounted from front now Mike !!)

Pictured Below
1st Panel = Filler
2nd Panel = RF Watt Meters for Forward (250W) and Reflected (5W) Output Power into Feed-line to Antanna
3ed Panel = Cabinet & Pallet Amp Heat Sink Temperatures, RF Power into Duplexers (250W), and Voltage & Current Meters for Pallet Amp
4th Panel = Pallet Amplifier
5th Panel = Holds Current Shunt for Pallet Amp. Meter on back

Pictured Below
1st Panel = Holds Current Shunt for Pallet Amp. Meter
2ed Panel = Back-up 80 Watt Power Amplifier (out of original 442.650 repeater from early 1979)
3ed Panel Shelf = 2 Equalizers for Repeater & Link Radio Audio
4th Panel = Micro Computer Concepts Controller
5th Panel = Kenwood TKR-850 Repeater
6th Panel Shelf = For holding the link radio
(10,6,& 220) and its Controller
7th Panel = Filler

Pictured Below
1st Panel Shelf = For holding the link radio & its Controller
3ed & 4th Panels = Fillers
4th Panel = Astron RM-60M 12 Volt Power Supply
Note: The 50 Volt Power Supply for the Pallet Amp is mounted above the Astron behind the big filler panel

Pictured Below
This is the back side of the cabinet and at the top is the TX-RX Vari-Notch 4 can Duplexers.  The 2 additional larger cans mounted below them are also
Pass/Notch Duplexers with one going to be installed between the exciter and final amplifier and the other after the amplifier and duplexers.  There will also be 2 more pass-cavities added in above the duplexers rack that will connected in before them and the receiver that need to be removed from the repeater in operation now.  A little over half way down there are 2 rack panels that provide a terminal breakout of all the connections from the controller and the repeater.  You can also see the 50 Volt power supply sitting above the Astron power supply at the bottom.



....Coming Alive ....


We Will Explain Later !!!


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